ARRANGEMENT AND PROCESS FOR THE CONSTRUCTION OF A STEEL PLANT AND RELATED STEEL PLANT

Abstract

The invention relates to an arrangement, in particular a construction site, and a process for the construction of a steel plant for the production of long or flat products and a related steel plant which includes its subdivision into areas of greater (H) or lesser load (L), wherein the loads of the area of lesser load (L) (<1.5 tons/m.sup.2) are placed on a raised plancher made of columns and slabs which have been prefabricated simultaneously with the construction of the building, which houses the production line of the steel plant, and the areas of greater load in a zone (PF; PC, C) which is preferably covered, adjacent to the construction zone of the building which includes a reinforcement production zone, a casting zone; and a curing zone. The post-tensioning technique of slabs is applied. The invention allows to speed up the construction of the steel plant.

Claims

1. An arrangement for the construction of a steel plant for the production of long products, in particular bars, wire rods, rails and the like, or for flat products, in particular strips, sheets and the like, comprising: (a) an arrangement for the construction of a building suitable for containing machinery of a casting and rolling line of said steel plant, wherein the areas accommodating said machinery are divided into two types of areas (L, H) according to the load they are to support, namely into an area for loads<1.5 tons/m.sup.2 (L) and an area for loads1.5 tons/m.sup.2 (H); (b) alongside said arrangement for the construction of said building a prefabrication area (PF; PC, C) of columns and slabs intended to make a raised plancher comprising: (b-1) a reinforcement construction zone for said columns and said slabs comprising bending machines (M, m) and shearing machines and materials for making reinforcement; (b-2) a zone for casting said columns and said slabs comprising a plurality of formworks for making said columns and said slabs; (b-3) a zone for storing and curing said columns and said slabs originating from said casting area; wherein the areas for loads<1.5 tons/m.sup.2 (L) within the construction zone of the building can be/are equipped with at least one foundation plate and/or plinths suitable for accommodating said columns made in the zones listed under point (b); (c) at least one movement device for transporting the reinforcements, the columns or the slabs from one zone of point (b) to another; (d) at least one device for transporting the columns and/or slabs from the zone of point (b-3) into the construction zone of the building.

2. The arrangement according to claim 1, wherein (I) the reinforcement construction zone, together with the casting zone, is substantially parallel to the storage and curing zone which, in turn, is arranged substantially parallel to said building construction zone; or that (II) the reinforcement construction zone, the casting zone and the storage and curing zone are aligned along a line which is arranged substantially parallel to said building construction zone.

3. The arrangement according to claim 1, wherein said movement device is selected among a rail-mounted gantry crane and a mobile crane with a radius of action of 360; and/or that said device for transporting the columns and slabs in the building construction zone is a self-propelled conveyor of the SPMT type.

4. The arrangement according to claim 3, wherein for the transport of the slabs, a lattice frame, in particular made of steel beams, is installed on the platform of the self-propelled vehicle, on the upper part of which, during use, at least two slabs are placed so as to raise the height thereof with respect to the ground so as to be at a height that exceeds by at least 20 cm the height of the column heads placed in the plinths and/or on the at least one foundation plate.

5. The arrangement according to claim 1, wherein said reinforcement construction zone comprises elements, in particular strands and respective sleeves, suitable for incorporation into said slabs for post-tensioning them.

6. The arrangement according to claim 1, further comprising at least one covering structure, in particular a marquee, housing said zones identified under (b-1) to (b-3).

7. A process for the construction of a steel plant for the production of long products, in particular bars, wire rods, rails and the like, or for flat products, in particular strips, sheets and the like, comprising the following steps: (i) providing an arrangement according to claim 1; (ii) at the same time as the construction of the building and the preparation of the areas (H) accommodating the parts of the steel plant with loads1.5 tons/m.sup.2, carrying out the following steps: (ii-1) pre-fabrication of a plurality of said columns; (ii-2) in the zone according to (b-1) production of reinforcements for said slabs wherein said reinforcements comprise elements, in particular strands contained in sleeves, for post-tensioning the slabs, (ii-3) in the zone according to (b-2) insertion of the reinforcements in the formworks for the slabs and casting of the slabs, (ii-4) after a first determined time, removal of the slabs from the formwork and transfer of the slabs to the zone according to (b-3); (ii-5) curing of the slabs in the zone according to (b-3) for a second predetermined time; (iii) construction of said at least one foundation plate and/or said plinths in the area(s) (L) that are to support loads< of 1.5 tons/m.sup.2; (iv) transferring said prefabricated columns to the area of said at least one foundation slab and/or said plinths and positioning and anchoring said columns in said at least one foundation slab and/or in said plinths; (v) transfer of said slabs cured in the area of the positioned and anchored columns and positioning of the slabs on the columns leaving spaces between the adjacent slabs; (vi) casting in place of the spaces completing the construction of a raised plancher; (vii) post-tensioning of said elements for post-tensioning.

8. A steel plant for the production of long products, in particular bars, wire rods, rails and the like, or flat products, in particular strips, sheets and the like, comprising: (A) two types of areas (H, L) subdivided according to the greater or lesser load to be supported, and specifically subdivided according to the criterion of supporting a load or <1.5 tons/m.sup.2, wherein in the greater load area (H) machines of the steel plant corresponding to a load1.5 tons/m.sup.2 are placed and in the lesser load area (L) machines of the steel plant corresponding to a load<1.5 tons/m.sup.2 are placed; (B) in the lesser load area (L) a structure containing at least one foundation plate and/or a plurality of plinths, a plurality of prefabricated columns placed at predetermined distances on the at least one foundation plate and/or in the plinths and a plurality of prefabricated slabs positioned above said columns with spaces between adjacent slabs to form a plancher; (C) machinery with a lower weight which is placed above said plancher, wherein said slabs comprise tensioned elements.

9. The plant according to claim 8, wherein said spaces are filled with a mortar casting.

10. The plant according to claim 8, wherein said slabs have a size less than or equal to 6.56.5 m and/or a weight not greater than 50 tons.

11. The arrangement according to claim 3, wherein said movement device is equipped with a platform that can be raised and lowered.

12. The arrangement according to claim 5, wherein the elements are corrugated.

13. The arrangement according to claim 6, wherein the at least one covering structure comprises a sliding awning.

14. The process of claim 7, wherein the first determined time is about one day.

15. The process of claim 7, wherein the second determined time is about four weeks.

16. The process of claim 7, wherein the step of post-tensioning of said elements for post-tensioning is with the aid of hydraulic jacks.

17. The process of claim 7, wherein after the step of (vii) further comprising the steps of: (viii) placement of the lower loads of the steel plant on said plancher; and (ix) placement of the higher loads of the steel plant in the area(s) (H) for the higher loads.

18. The steel plant of claim 8, wherein said tensioned elements comprise strands in relative sleeves filled with cement mortar.

Description

DESCRIPTION OF PREFERRED EMBODIMENT EXAMPLES

[0080] FIG. 1a depicts in a top view a steel plant for the production of long products according to the state of the art.

[0081] FIGS. 1b-d depict the steel plant for the production of long products according to FIG. 1a in which the zones of different load demands are identified and in which a prefabrication area is provided according to a first embodiment (FIG. 1b) of the invention; a prefabrication area according to a second embodiment (FIG. 1c) of the invention; and in which the flows of the prefabricated elements according to one of the two embodiments of FIGS. 1b and 1c (FIG. 1d) are highlighted.

[0082] FIG. 2a depicts in detail the casting and curing area of the slabs of the embodiment according to FIG. 1b.

[0083] FIG. 2b depicts in detail the casting and curing area of the slabs of the embodiment according to FIG. 1c.

[0084] FIG. 3 shows an embodiment example for a sequence of working steps of the process according to the invention in accordance with FIG. 2b.

[0085] FIGS. 4a-c show in two perspective views (FIG. 4a; FIG. 4b) the construction of the plancher on a series of already installed columns of a steel plant for co-rolling; and an assembly of a foundation plate with columns supporting a plurality of slabs.

[0086] FIGS. 5a/b are two plan views, the first (FIG. 5a) of a foundation plate with plinths to accommodate columns; and the second (FIG. 5b) of the laying of the columns in the relative plinths included in FIG. 5a.

[0087] FIG. 6 shows in section an embodiment example of the anchoring of a column in the foundation plate.

[0088] FIG. 7 shows in section the three levels (foundation plate, columns, slabs) of a plancher raised according to the invention.

[0089] FIG. 8 shows in a top view four slabs placed on the columns of FIG. 5b highlighting the presence of elements for post-tensioning inside the slabs.

[0090] FIGS. 9a/b show in section a part of a slab along a post-tensioning element highlighting two different states of tensioning thereof (FIG. 9a, relaxed; FIG. 9b, taut).

[0091] FIGS. 10a-c show in section three columns of different position inside the structure according to FIGS. 7 and 8 (FIG. 10a: central; FIG. 10b: corner; FIG. 10c: side edge).

[0092] FIG. 11 shows details of the top of the column according to FIG. 10a with details for the support of a jack or of a slab.

[0093] FIGS. 12a-c show in section (FIGS. 12a and 12b) the system for introducing mortar into the metal sleeves of post-tensioning elements; and in a transparent perspective view a pull point of a strand in a sleeve.

[0094] FIGS. 13a-c show a comparison between two plancher structures raised according to the state of the art (FIGS. 13a and b) and the structure according to the invention (FIG. 13c).

[0095] FIG. 1a shows the layout of a rolling plant for long products according to the state of the art. In FIGS. 1b to 1d, the dotted area highlights the areas subject to light loads L, i.e., loads not exceeding 1.5 tons/m.sup.2, while the hatched area highlights the areas H subject to heavy loads, i.e., loads exceeding 1.5 tons/m.sup.2 and which can reach up to 3 tons/m.sup.2, or subject to very high concentrated loads due to the machines themselves. The structure which supports such loads, or the plancher, can be adapted to weight needs by providing simpler building structures for smaller loads. The total black area shows that at least 50% of the total plancher is affected by the aforesaid light loads and therefore it is possible to construct it with prefabricated slabs.

[0096] In this regard, the invention proposes a construction site for the prefabrication of the necessary slabs and columns directly in situ, in particular in a zone placed laterally to the construction zone of the building for the steel plant (FIGS. 1b and 1c). Advantageously, the prefabrication area PF is covered and set up in an adjacent and central position with respect to what will be the final layout of the plant.

[0097] Said area PF is divided into an area PC for the construction of the structures (slabs and columns) and a curing area C thereof. The fact of being able to operate in a zone adjacent to the place of construction of the building in a covered area, allows carrying out the activities in any weather condition and facilitating the transport of the structures.

[0098] The construction method of the structures for the plancher involves the following steps in the precast PC area: [0099] 1. Construction of the metal reinforcement starting from bars and rolls of steel rod in an area provided with straightening, bending and shearing machines. [0100] 2. Construction of the metal formworks (or casings) of the desired size and insertion of the metal reinforcement. [0101] 3. Placement of sleeves, or ducts, intended to contain the cables for post-tensioning, in the reinforcement for the slabs. [0102] 4. Concrete casting in the formworks. [0103] 5. Repeating steps 1 to 4 until one or two structures have been placed.

[0104] At the end of the concrete setting (about 24 h), the structures are taken by crane and placed in the curing area C (about 28 days). The slabs are stacked in the curing area up to four slabs on top of each other. Further storage areas ST can then be included for finished and hardened structures.

[0105] In accordance with a first embodiment, the curing area of the structures is arranged next to that of prefabrication (FIG. 1b), arranging the areas PC and C side by side in parallel, while in accordance with a second embodiment the two areas PC and C are aligned and placed in succession (FIG. 1c).

[0106] The arrows in FIG. 1d illustrate the transport flows of the structures originating from the prefabrication zone PF in the respective areas L subject to a lower load.

[0107] This offline arrangement of the prefabrication and curing area allows the construction operations of the prefabricated structures to be performed temporally in parallel with the construction of the foundation posts and the support plinths of the building, with evident time savings. The prefabrication areas PF are described in detail below:

[0108] FIG. 2a shows a detail of the first embodiment and represents the construction of the slabs in which the formworks are arranged on two rows R.sub.1 and R.sub.2 leaving a central passage 2 to allow the transit of one or more concrete mixers 4 which perform the concrete casting in the formworks. The positions 6 for pre-assembling the reinforcements of the blocks or slabs, the positions 8 of the casting of the slabs in the formworks and the positions 10 for curing the slabs are distinguished. The necessary machinery, such as bending machines, straightening machines, shearing machines, to construct the reinforcements are positioned in zone M. Vehicles V are included for unloading straight bars and steel rod coils. The positions 6 and 8 are located below two sliding tent buildings 12a and 12b. A mobile crane 14 with a 360 radius of action (dashed circle) allows the movement of the slabs from the zone PC to the zone C and the movement of the reinforcements in the formworks. An SPMT 16, i.e., a platform vehicle with a wide series of independently operable wheels for transporting bulky loads for on-site construction, is waiting for the ready slabs to carry them into the building under construction in the lower load areas.

[0109] FIG. 2b instead shows a detail of the second embodiment, always related to the construction of the slabs, in which the formworks are arranged on a single row R and the transit of the concrete mixers 4 which perform the concrete casting occurs on one of the two sides of the row R. The machinery necessary, as specified above, to construct the reinforcements is located in the zone m, where the unloading (not depicted) of steel bars and steel rod coils also occurs. Gantry cranes 18 sliding on rails are included for moving the parts between the various zones. From right to left follow reinforcement pre-assembly positions 106, slab casting positions 108 and concrete curing positions 110. All the positions are contained in a tent building 112. An SPMT 16 waits for the slabs, ready to take them to the planned building for the construction of the plancher(s) in the lower load areas.

[0110] The initial hardening of the concrete lasts about 24 hours and leads the material to acquire a consistency and resistance which allows the movement thereof. The curing instead occurs in about 28 days (4 weeks) and brings the concrete to assume its final mechanical features. The structures are moved from the zone PC to the zone C after approximately 24 hours.

[0111] With reference to the layout of FIG. 2a, at the end of the initial concrete hardening, a truck-crane 14 withdraws the slabs from the prefabrication area and places them in a lateral storage area C for the curing step. The lifting of the slab is performed carried out using, for example, four lifting hooks (lifting beam) anchored in the slab which have been previously arranged. Up to four slabs are superimposed in the curing area to optimize the space, positioning them while taking into account the assembly sequence.

[0112] With reference to the layout variant of FIG. 2b and FIG. 3, at the end of the concrete setting step, a mobile gantry crane 18 withdraws the slabs from the prefabrication area PC and positions them in a facing curing area C. The movement operations of the finished hardened slabs are performed as in the previous case.

[0113] At the end of the concrete curing step (after about 28 days), the slabs and columns are ready to be positioned in the various areas where the structures of the prefabricated plancher are to be laid. The slabs are loaded onto a self-propelled modular transporter (SPMT) 16. The self-propelled vehicle has the possibility to steer the wheels 360 degrees. This allows carousel and lateral movements. The height of the platform can be adjusted hydraulically, allowing the vertical lifting or lowering of the load.

[0114] A flow diagram of the embodiment according to FIG. 2b is found, integrated with the assembly step of the plancher structure in FIG. 3. The progress of the works is indicated by the arrows. The start is given by the positions 106 for the prefabrication of the reinforcements, with a machine m for bending and the cutting of rods in the zone. Gantry cranes 18 withdraw the reinforcements and move them to the positions 108 of the slab casting zone with concrete provided by concrete mixers 4. After 24 hours the slabs are extracted from the formworks and moved with relative gantry cranes 18 to the positions 110 for curing, each position can receive four slabs 20. The hardened slabs are lifted and placed on an SPMT 16 with a gantry crane 18. Advantageously, for the transport of the slabs, a steel beam lattice frame 22 is installed on the platform of the self-propelled vehicle 16 on the upper part of which the slabs are supported (FIG. 4a and FIG. 4b) so as to raise the height thereof with respect to the ground so that they are at a height which exceeds the height of the heads of the previously installed prefabricated columns 24 by at least 20 cm.

[0115] The loading of the slabs 20 on the lattice 22 of the self-propelled vehicle 16 can occur with a gantry crane 16 or with a mobile crane 14, depending on whether it is the layout of FIG. 2a or the layout of FIGS. 2b, 3, respectively.

[0116] At least two slabs 20 are placed on the lattice 22 and when the self-propelled vehicle 16 is positioned between two rows of columns 24, the mobile platform 28 of the self-propelled vehicle 16 is lowered and the edges of the slabs 20 simultaneously rest on the heads of the columns 24 already positioned.

[0117] The slabs are then carefully levelled using hydraulic jacks (not depicted).

[0118] FIG. 4c shows slabs positioned on columns 24 anchored in a foundation plate 30. The positioning of the slabs 20 on the columns 24 is done in such a way as to leave a suitable space 32, for example of about 30 cm, between adjacent slabs 20; the slabs 20 are then constrained to the columns 24 by means of embedded anchor bolts and/or shear keys (not depicted) and finally are joined together and with the columns 24 with a concrete casting in place, which will thereby form a cross joint in the spaces 32. The anchor bolts are threaded bars with steel end plates, to be anchored in the casting by means of positioning jigs and are applied to anchor the prefabricated load-bearing structure to the reinforced concrete slabs. A shear key is a tubular steel profile embedded in the casting of a constraint block so as to absorb mainly shearing actions, leaving the axial action and bending moments almost unchanged.

[0119] The composition of the load-bearing structure is illustrated in more detail below. FIG. 5a shows a foundation plate in which plinths 34 are included to accommodate prefabricated columns (not depicted). In FIG. 5b the columns 24 positioned in the plinths of FIG. 5a can already be seen.

[0120] FIG. 6 shows how a column 24 is anchored in the foundation plate 30 which is in turn supported on a lean layer 31. Corrugated metal sleeves 36 are provided in the plate 30, which receive the ends of the reinforcements 44 immersed in the column 24. A centring device 42 allows the correct positioning of the column 24. The sides 40 are used for grouting (i.e., rejointing of the joints). A casting of shrinkage-compensating mortar 38 serves to further fasten the column 24 in the plate 30.

[0121] FIG. 7 shows the composition of the finished load-bearing structure in section: Columns 24 bearing slabs 20 have been erected on the foundation plate 30 with lean mortar 31. FIG. 8 shows four slabs 20 forming a square in which the cross spaces 32 are filled with a mortar casting to connect the slabs 20. The slabs contain a set of cables or strands for tensioning the slab 20.

[0122] After the installation of the prefabricated slab 20 on the columns 24, the post-tensioning of the post-tensioning elements 46 is performed, for example by means of hydraulic jacks which tension cables inside flexible sleeves by applying, to the release of the cable, a compression action on the entire structure. When the slab 20 is tensioned with the post-tensioning method, this means that the steel strand is tensioned and the concrete is compressed. In order to avoid cutting the post-tensioning strands during drilling on site, dedicated positions (highlighted areas) must be identified and marked during the design step.

[0123] The elongation of the steel is measured and recorded for each strand 46 (a dedicated tensioning plane is envisaged for each single strand) to determine and verify that the tensioning force respects the design parameters. Once the correct elongation has been achieved, the strand 46 is locked in place, the tails of the steel cables can be cut and the sleeve surrounding the strand 46 is filled with anti-shrinkage mortar to provide coverage and protection.

[0124] The post-tensioning thus allows to reduce the overall thickness of the slab 20 and the amount of reinforcement, therefore with an overall saving of weights and costs (minimizes its own weight and the foundation loads). In particular, in the case of the plancher object of the invention, the post-tensioned slab 20, with the same supported load, may have a thickness of 500 mm instead of 800 mm of that made on site according to the traditional method.

[0125] FIGS. 9a and 9b show a section through a slab 20 with a relaxed strand 46a (FIG. 9a) and a tensioned strand 46b (FIG. 9b) with respect to a horizontal line h. The drawings do not show any reductions in thickness. In the points x there is the possibility of mortar injection into the sleeves surrounding the strands.

[0126] The process according to the invention includes the construction of the foundation plates and/or of relative plinths, the prefabrication of the columns and of the slabs, the positioning of the columns in the plate and/or in the plinths and then the positioning of the slabs on the columns.

[0127] The levelling of the slabs preferably occurs with hydraulic jacks, the slabs (blocks) are connected with a casting in place, and thereafter the post-tensioning of the tensioning elements is advantageously carried out.

[0128] Machinery necessary for the prefabrication of the structures are for example a 360 mobile crane, an SPMT, a covered building with a sliding tent, a forklift and a machine for bending rods for reinforced concrete. For the installation of the prefabricated columns, a forklift and a transporter truck are needed (possibly an SPMT can be used), while for the positioning of the slabs on the columns, an SPMT with lattice and hydraulic jacks are needed.

[0129] FIGS. 10a to 10c show columns which change appearance slightly with respect to the construction of their heads. FIG. 10a illustrates a column 24a to be placed in the centre of the cross formed between four slabs 20, FIG. 10b a column 24b to be placed on the corner of one slab 20 (with an enlargement of the circled part) and FIG. 10c a column 24c to be placed on the edge of the plancher between two slabs 20. The anchoring of the columns in the plate 30 has been described with reference to FIG. 6 and is not illustrated here again.

[0130] At this point it will also be said that the same or similar elements bear the same reference numerals even in different figures and are usually not described again if they have already been described with reference to a previous figure.

[0131] The numeral 46 can generally refer to a pre-tensioning element, to the sleeve containing a strand or to the strand itself. For fastening the slabs 20, plates are provided with shear key 48 anchored in the column 24a always with the aid of shrinkage mortar and anchoring pins 52 connected to, or forming a single piece with, the plate with the shear key. In addition, plates 54 are noted for the lifting jack fastened by a horizontal element 56. An anchoring bolt 58 for example of the Halfen type or the like helps to fasten the slab 20 on the column 24b. FIG. 10b shows the strand or the relative sleeve 46.

[0132] FIG. 11 shows more details of the head of a column. Note the plates 54 for supporting the lifting jack and the steel tube 56 for connecting the plates 54 to the column 24. The clamps 60 fastened with an extended nut and two platelets are used to fasten the slab 20 according to a prefabricated block support system and with variable adjustment.

[0133] FIGS. 12a and 12b show details of the pull and anchoring system with strands, and precisely the anchoring head (FIG. 12a) and the joint between metal sleeves, respectively. In the slab 20 the strand slides inside its metal sleeve 46. A fastening cone 62 allows the splicing of two sectors of sleeve 46. A succession of a valve 64, a plastic corrugated tube 66, a connector 68, a plug 70 and a saddle 72 (depicted in an exploded view) fastened with shrinkage mortar 74 in the slab 20 allow filling the sleeve 46 with mortar. Similarly, the filling with mortar occurs on the head 45 with a succession (idem in exploded view) of a valve 76, a corrugated plastic tube 78 and a cap 80 fastened with mortar in a hole 84 of the slab 20. FIG. 12c repeats in an exploded perspective view a head 45 accommodated in a plate inside a hole 84 of the slab and connected to the sleeve 46 for accommodating a strand. Parts of the classic reinforcement 47 of the slab 20 are noted.

[0134] Finally, FIGS. 13a to 13c compare the state of the art (FIGS. 13a and 13b) with the system according to the invention (FIG. 13c). FIG. 13a shows a traditional cast-in-situ solution with a foundation plate 130 and a raised floor with parts of considerable thickness. Three levels of props and formworks 124a, 124b, and 124c are required. FIG. 13b depicts a solution with a slab lightened with predalles. Predalles slabs are flat slabs of prefabricated, slowly reinforced latticed concrete, which are used for the construction of slab concrete floors. Only one set of props 124d without formworks is needed. The foundation plate 230 is similar to that 30 foreseen for the invention. All three forms have columns (24, 124, 224). The invention (FIG. 13c) avoids the use of props (barred lines) with the columns 24 and especially the relatively thin and tensioned slabs 20.

[0135] Table 1 below compares the construction times of the floor according to the traditional method, according to a method with lightened floor and in situ casting, and the plancher according to the invention.

TABLE-US-00001 TABLE 1 Parameter Traditional method Lightened floor Invention On-site execution 14-17 hours/m.sup.3 9-11 hours/m.sup.3 5-6 hours/m.sup.3 speed (civil rendering) Mandatory Poles-plinths- Poles-plinths- The columns and production sequence foundations- foundations- slabs can be made columns-beams- columns-beams- off-line, in parallel floors floors, but slabs with with the construction predalles than can be of the pre-fabricated in plinths/foundations. parallel Poles* [00001] [00002] [00003] Plinths* [00004] [00005] [00006] Precast civil works* (0) [00007] [00008] Cast-in-situ civil works* [00009] [00010] [00011] End of civil works M** 10 M 8 M 5.5 from the beginning of the plinths End of civil works M 12.5 M 10.5 M 6.5 from the beginning of the poles Beginning of plant M 10.5 M 9 M 6.5 construction installations Costs (/m.sup.2) 500 580 550-600 From left to right there is a considerable reduction in construction times. *The extensions of the black bars show the periods needed for works indicated in the left-most column and the position of the bars relative to each other within a column shows whether the works can be performed in parallel or one after another. **M = Months

[0136] As can be seen, the construction step of the prefabricated structures (slabs and columns), referred to as pre-cast civil works in Table 1, can begin substantially at the same time as the construction of the plinths begins. The next step of cast-in-situ civil works, which is related to the construction of the in situ castings of the remaining parts of the plant, is decidedly reduced with respect to the conventional methods.

[0137] Overall, the fabrication method of the raised plancher according to the invention allows to save about 40% of the time needed with respect to the traditional method. The higher costs of the slab fabrication technique with respect to the conventional methods are reabsorbed by the greater execution speed of the civil works.